^>  //.  b'j--:-^^jK 


STATE  Pl^'T  BOARD 


Issued  November  25,  1010. 


U.  S.  DEPARTMENT    OF   ACxRICULTURE. 
BUREAU   OF   ENTOMOLOGY— CIRCULAR  No.  129. 

L.  O.  HOWARD.   Entomologist  and  Chief  of  Bureau. 


INSECTS  IN  THEIR  RELATION  TO  THE  REDUCTION 
.  OF  FUTURE  SUPPLIES  OF  TIMBER,  AND 
GENERAL  PRINCIPLES  OF  CONTROL. 


BY 


A.  D.  HOPKINS, 

In  Charge  of  Forest  Insect  Investigations. 


64130°  —  (Jir.  ll!0 — 10  Washington  :  government  printing  ofrce  :  1910 


BUREAU  OF  ENTOMOLOGY. 

L.  O.  Howard,  Entomologist  ami  Cliicf  of  Bureau. 

C.  L.  Marlatt,  Assistant  Entomologist  and  Acting  Chief  in  Absence  of  Chief. 

R.    S.  Clifton,   Executive  Assistant. 

W.  V.  Tastei,  Chief  Clerk. 

F.  IT.  Chittenden, in  charge  of  truck  crop  and  stored  product  insect  investigations. 

A.  D.  Hopkins,  in  charge  of  forest  insect  investigations. 

W.  D.  Hunter,  in  charge  of  southern  field  crop  insect  investigations. 

F.  M.  Webster,  in  charge  of  cereal  and  forage  insect  investigations. 

A.  I..  QuAiNTANCE,  in  charge  of  deciduous  fruit  insect  investigations. 

E.  F.  Phillips,  in  charge  of  bee  culture. 

I).  M.  Rogers,  i)i  charge  of  preventing  spread  of  moths,  field  ivork. 

RoLLA  P.  CuRRiE,  in  charge  of  editorial  work. 

Mabel  Colcord,  librarian. 

Forest  Insect  Investigations. 

A.  I).  Hopkins,  in  charge. 

H.  E.  Burke,  J.  L.  Webb,  Josef  Brunner,  S.  A.  Rohwer,  T.  E.  Snyder,  W.  D. 

Edmonston,  agents  and  experts. 
Mary  E.  Faunce,  preparator. 

William  Middleton,  Mary  C.  Johnson,  student  assistants. 
II 


Circular  No.  129.  Issued  November  25, 1910. 

United  States  Department  of  Agriculture, 

BUREAU  OF  ENTOMOLOGY. 

L.  O.  HOWARD,   Entomologist  and   Chief  of  Bureau. 


INSECTS  IN  THEIR  RELATION  TO  THE  REDUCTION  OF 
FUTURE  SUPPLIES  OF  TI3IBER,  AND  GENERAL  PRIN- 
CIPLES OF  CONTROL.^ 

By  A.  D.  Hopkins, 

In  Charge  of  Forest  Insect  Investigations. 

Insects  not  only  reduce  future  supplies  of  timber  by  killing  the  ma- 
ture trees  and  destroying  the  wood  of  timber  that  is  inaccessible  for 
utilization,  but  through  injuries  inflicted  upon  trees  during  the  flow- 
ering, fruiting,  germinating,  seedling,  and  sapling  periods  of  early 
growth  they  prevent  normal  reproduction  and  development. 

INTERRELATIONS  OF  FOREST  INSECTS  AND  FOREST  FIRES. 

Investigations  conducted  by  the  Avriter  and  assistants  in  all  sections 
of  the  country  during  the  past  ten  years  indicate  to  them  quite  con- 
clusively that  the  average  percentage  of  loss  of  merchantable  timber 
in  the  forests  of  the  entire  country  to  be  charged  to  insects  during  a 
five  or  ten  year  period  is  infinitely  greater  than  most  people  realize. 

Losses  from  forest  insects. — The  writer  estimates  that  for  a  ten- 
year  period  the  average  amount  of  timber  in  the  forests  of  the  entire 
country  killed  and  reduced  in  value  by  insects  would  represent  an 
average  loss  of  $02,500,000  annually.^ 

It  has  been  estimated  that  the  Black  Hills  beetle  killed  approxi- 
mately 1,000,000,000  feet  B.  M.  of  timber  during  a  period  of  ten  years, 
which  at  $2.50  per  thousand  would  amount  to  an  average  of  $250,000 
annually.  This  is  merely  one  example  of  very  destructive  depreda- 
tions by  a  single  species  of  barkbeetle  in  a  single  National  Forest.*^ 

°  Revised  extracts  from  Bulletin  No.  58,  Part  V,  Bureau  of  Entomology, 
United  States  Department  of  Agriculture. 

^Losses  from  forest  fires. — It  has  been  estimated  that  "on  the  average,  since 
1870,  forest  fires  have  yearly  cost  $50,000,000  in  timber."  (Cleveland,  T.,  jr.. 
Circular  167,  Forest  Service,  United  States  Department  of  Agriculture,  p.  3.) 

^  It  has  been  estimated  that  the  losses  of  timber  from  forest  fires  on  all  of 
the  National  Forests  of  the  United  States  from  1905  to  1908,  inclusive,  average 
only  $105,002  annually.  (Cleveland,  T.,  jr..  Yearbook  United  States  Department 
of  Agriculture  for  1908,  p.  541.) 


2  INSECTS   AND  REDUCED  TIMBER  SUPPLY. 

Prof.  Lawrence  Brimer,  state  entomologist  of  Nebraska,  at  a  meet- 
ing of  the  American  Association  of  Economic  Entomologists,  held  at 
Baltimore,  Md.,  in  December,  1908,  spoke  as  follows:  "I  can  agree 
with  Doctor  Hopkins  that  the  insects  are  far  more  important  in 
destroying  our  forests  than  fires." 

Insect-hilled  thiiber  as  fuel  for  fres. — It  has  often  happened  that 
after  insects  have  Irilled  the  timber  over  extensive  areas  the  standing 
and  fallen  dead  trees  furnished  fuel  for  great  forest  fires  which  have 
not  onlv  destroved  or  charred  the  dead  timber  but  killed  the  livinor 
timber  and  reproduction  and  swept  on  into  adjacent  areas  of  healthy 
timber.  Indeed,  abundant  evidence  has  been  found  during  recent  in- 
vestigations to  indicate  that  some  of  the  vast  denuded  areas  in  the 
Rocky  ^Mountains  and  other  sections  of  the  country  are  primarily  due 
to  widespread  devastation  by  insects,  and  that  subsequent  fires  de- 
stroyed the  timber  and  prevented  reproduction. 

It  is  also  evident'that  a  considerable  percentage  of  dead  timber,  and 
especially  that  found  in  coniferous  forest  regions,  which  has  generally 
been  believed  to  have  been  fire-killed  is  a  result  of  primary  attack  by 
insects.  This  has  been  demonstrated  in  many  cases  by  the  pitch- 
marked  galleries  of  the  destructive  barkbeetles  on  the  surface  of  the 
wood  of  the  old  dead  trees  which  had  escaped  subsequent  fires. 

Fire-killed  timber  injured  hy  insects. — It  is  true  that  a  vast  amount 
of  timber  has  been  killed  outright  or  has  died  as  the  direct  result  of 
forest  fires,  but  in  almost  every  case  observed  insects  have  contributed 
to  a  greater  or  less  extent  to  the  death  of  recently  fire-injured  trees 
which  might  otherwise  have  recovered,  and  especially  to  the  rapid 
deterioration  of  the  wood  of  a  large  percentage  of  the  injured  and 
killed  trees.  It  is  evident  that  in  some  cases  fire-scorched  and  fire- 
killed  timber  has  contributed  to  the  multiplication  of  (me  or  more  of 
the  insect  enemies  destructive  to  living  timber,  and  thus  the  injury 
started  by  the  fire  may  have  resulted  in  a  destructive  outbreak  of 
beetles.  However,  it  is  evident  that  this  has  happened  only  when  the 
destructive  beetle  was  already  present  in  abnormal  numbers  in  the 
forest  surrounding  the  fire-swept  area.  Therefore,  it  is  believed 
that  injuries  by  fire  are  not  as  a  ride  an  hnpovtant  factor  in  contrib- 
uting to  sid)Si'(picnt  depredations  by  bavlxbeetles.  Such  fires,  how- 
ever, contribute  to  the  muhii)lication  of  the  insects  which  doj^rodate 
on  the  bai'k  and  wood  of  dying  antl  dead  trees,  so  tliat  in  forested 
areas  where  fires  are  fre(juent  the  damage  to  the  wood  of  such  trees 
is  more  severe,  and  fewer  injured  trees  recover  on  account  of  the 
al)nii(lance  of  seconchiry  })arkbeetle  eneujicvs  wliich  do  not,  as  a  rule, 
attack  and  kill  living  timber. 

Destruction  of  in^Hccts  by  fre. — Tliere  is  anotliei-  important  f(Miture 
in  the  relation  of  insects  and  fii-e,  in  which  the  lire  contributes  to  the 
destruction  of  the  i)rincipal  l)Mrkl>(H't le  enemies  of  the  living  timber, 

ICir.  II'JJJ 


INSECTS   AXD   REDUCED    TIMBER   SUPPLY.  .  3 

This  happens  when  the  fire  burns  the  timber  while  it  is  infested,  thus 
effectually  destroying  the  broods  of  the  insects.  It  is  perfectly  plain 
that  the  dying  and  dead  foliage  of  the  beetle-infested  trees  and  the 
dead  bark  on  the  trunks  would  cdntribute  to  the  spreading  of  crown 
fires  and  thus  the  bark  on  the  entire  infested  trunks  would  be  suffi- 
cienth^  scorched  to  kill  the  insects.  Therefore,  complete  fire  control 
may  easily  contribute  to  more  extended  depredations  by  insects  on  the 
living  timber,  thus  increasing,  rather  than  diminishing,  the  need  for 
insect  control.  However,  the  setting  of  fires  or  permitting  them  to 
burn  for  the  purpose  of  combating  insects  should  never  be  undertaken 
or  permitted. 

Durability  of  insect-hilled  timber. — Some  of  the  matured  larch 
trees  which  evidently  died  as  a  result  of  defoliation  by  the  larch 
worm  between  1881  and  1885,  and  which  had  escaped  subsequent 
depredations  b}^  fire  and  wood-boring  insects,  were  found  by  the 
writer  in  1908  to  be  standing  and  sound  enough  to  be  utilized  for 
railroad  ties  and  many  other  purposes.  Under  similar  conditions  the 
heart  wood  of  red  spruce  and  white  pine  in  the  East,  of  Engelmann 
spruce  in  the  Rocky  Mountains,  and  of  Douglas  fir  in  the  XortliAvest 
coast  region  have  been  found  by  the  writer  to  be  sound  enough  for 
profitable  utilization  for  pulp  wood,  lumber,  fuel,  and  other  pur- 
poses from  twenty  to  thirty  years  after  it  had  been  killed  by  insects 
or  fire.  Thus  it  is  shown  that  timber  killed  by  insects  and  fire  would 
be  available  for  utilization  for  many  years  were  it  not  for  injuries 
through  the  secondary  attacks  of  wood-boring  insects  and  the  de- 
struction of  insect-killed  timber  by  forest  fires. 

*  INTERRELATION     OF     FOREST     INSECTS    AND    FOREST    FUNGI. 

Decay  following  injury  by  insects. — It  is  well  known  that  the  bur- 
rows in  the  bark  and  wood  of  living  and  dead  trees  and  in  the  crude 
and  finished  products  often  contribute  to  the  entrance  of  bark  and 
wood  decaying  fungi.  Deterioration  and  decay  are  thus  far  more 
rapid  than  would  otherwise  be  possible.  It  is  also  knoAvn  that  trees 
injured  and  dying  from  primary  attack  by  parasitic  fungi  are  attrac- 
tive to  certain  insects  which  breed  in  the  bark  and  wood  of  sickly  and 
dying  trees,  and  that  certain  other  complicated  troubles  affecting  for- 
est trees  are  the  result  of  an  intimate  interrelation  and  interdepend- 
ence of  insects  and  fungi.  There  can  be  no  doubt,  however,  that  cer- 
tain species  and  groups  of  both  insects  and  fungi  are  independently 
capable  of  attacking  and  killing  perfectly  vigorous  and  healthy  trees. 

SUMMARY    AND    ESTIMATES    RELATING     TO     CHARACTER    AND    EXTENT    OF 

INSECT    DAMAGE.    . 

The  killing  of  trees  by  insects;  the  damage  by  them  to  the  wood 
of  living,  dying,  and  dead  timber;  the  destruction  of  insect-killed 
timber  by  subsequent  forest  fires;  the  damage  to  fire-killed  timber 

[Cir.  129] 


4.  INSECTS   AND  REDUCED   TIMBER   SUPPLY. 

by  insects;  and  the  damage  from  deca}^  resulting  from  insect  injuries 
to  the  wood,  have  all  been  more  or  less  continuous  for  centuries  and 
are  still  going  on  in  the  forest  and  woodland  areas  of  this  country. 

"^Miile  these  depredations  are  not  always  evident  or  important  in 
all  forests  or  localities,  yet  almost  every  year,  somewhere  in  the 
forests  of  the  country,  there  are  widespread  depredations. 

In  every  forest  and  woodland  there  is  an  ever  present  but  incon- 
spicuous army  of  insects  Avhich  require  the  bark,  wood,  foliage,  and 
seeds  of  the  various  tree  species  for  their  breeding  places  or  food. 
Thus,  the  accumulated  but  inconspicuous  injuries  wrought  during 
the  period  required  for  the  growth  of  a  tree  to  commercial  size  go 
far  toward  reducing  the  average  annual  increment  below  the  point 
of  profitable  investments. 

The  accumulated  damage  to  crude,  finished,  and  utilized  products 
reduces  the  profits  of  the  manufacturer,  increases  the  price  of  the 
higher  grades  to  the  consumer,  and  results  in  an  increased  drain  on 
the  natural  resources. 

In  any  attempt  to  estimate  in  feet^  hoard  measure^  or  dollars^  the 
extent  of  losses  or  waste  of  timber  supplies  caused  by  insects  there 
are  many  conflicting  factors  which  contribute  to  the  difficulty  of  ar- 
riving at  accurate  conclusions.  The  published  information  concern- 
ing the  amount  in  board  feet  of  standing  timber  in  the  country  is 
admittedly  only  an  estimate,  as  are  also  the  published  data  relating 
to  average  stumpage  value.  The  published  statistics  relating  to  the 
amount  and  value  of  forest  products  are  of  course  more  accurate,  but 
until  more  complete  data  can  be  furnished  by  the  forest  experts  on 
the  various  complicated  phases  of  forest  statistics  any  figures  given 
by  the  forest  entomologist  relating  to  the  value  of  timber  and  com- 
mercial products  destroyed  or  reduced  in  value  by  insects  must  be 
considered  on  the  same  basis  as  the  other  estimates,  and  as  the  test 
that  can  be  presented  on  available  evidence. 

Standing  timbei'  hilled  and  damaged  hy  insects. — When  we  con- 
sider the  amount  of  standing  merchantable  timber  killed  by  insects 
and  the  amount  of  standing  timber,  living,  dying,  and  dead,  which 
has  been  reduced  in  quantity  and  value  through  their  agency  during 
a  ten-year  period,  we  would  estimate  that  such  timber  represents  an 
equivalent  of  more  than  10  per  cent  of  the  quantity  and  stumpage 
value  of  the  total  stand  of  merchantable  timber  in  the  United  States 
at  any  given  time."     A  certain  percentage  of  such  timber  is  a  total 

oThe  estimate  of  the  area  and  stand  of  the  present  forests  of  the  United 

States,  as  piven  in  Circular  KH;  of  llio  Forost  Sorvico,  pajxo  (>,  is  two  trillion 
{ivo  hundred  billion  feet  (2,r>()().()<K),()()(),()()())  board  nioMSuro.  The  average 
stunipaj^'e  value  has  boon  ^iven  as  .$2. HO  \)vv  one  thousand  foot  1).  ni.,  niakinj;  a 
total  value  of  tho  standing'  nierchantablo  timber  of  .$(;,12r>(MKM),()()0.  Ten  i)er 
cent  of  this  anjoniil  would  be  .$(;2r),(M)(),000,  jis  the  amount  to  be  charj^ed  to  in- 
inr.  I'J't] 


INSECTS  AND   REDUCED   TIMBER  SUPPLY.  5 

loss  because  of  the  impossibility  of  utilization;  but  in  some  cases  a 
greater  or  less  percentage  can  be,  and  in  some  cases  is,  utilized  within 
the  period  in  which  it  is  of  sufficient  value  to  yield  a  profitable  return 
on  the  cost  of  logging  and  manufacture,  although  its  value  is  greatly 
reduced. 

Reduction  iyi  the  Nation's  wealth. — AYhen  we  consider  the  forest 
resources  both  in  merchantable  timber  and  young  growth  as  an  im- 
portant asset  of  the  Nation's  wealth;  as  representing  a  given  value 
to  the  people  for  direct  utilization ;  as  a  cover  to  the  soil  for  protec- 
tion of  the  land  from  erosion ;  as  protection  of  headwater  streams  and 
of  game;  and  as  contributing  to  the  aisthetic  value  of  health  and 
pleasure  resorts,  it  would  be  difficult  indeed  to  estimate  the  amount 
or  percentage  of  loss  of  timber  or  the  reduction  in  the  land  values,  in 
each  case,  chargeable  to  iusects.  It  is  plain,  however,  that  in  the 
aggregate  it  is  considerably  greater  than  when  estimated  on  stumpage 
values  alone. 

Reduction  in  cash  revenue. — When  we  consider  the  problem  from 
the  standpoint  of  direct  utilization  we  can  estimate  the  annual  loss 
on  a  basis  of  mill  values;  but  here  again  we  meet  with  complications, 
since  much  of  the  damaged  material  is  left  standing  or  is  discarded 
in  the  woods  or  at  the  mill  without  measurement.  Therefore  we  are 
left  to  judge  from  our  observ^ations  and  loiowledge  of  the  general 
conditions  as  regards  dead  and  damaged  timber  found  in  the  forests 
of  the  country,  and  the  information  from  lumbermen  in  different  sec- 
tions, as  to  the  percentage  of  loss  from  defective  timber.  On  this 
basis  we  can  estimate  that  the  amount  of  insect-killed  and  damaged 
timber  left  in  the  woods,  plus  the  reduction  in  value  of  that  utilized, 
to  be  charged  to  insects  is  not  far  from  an  equivalent  of  10  per  cent 
of  the  value  of  the  annual  output  of  forest  products  of  all  kinds,  in 
the  rough.  The  total  value  of  the  forest  products  of  the  United 
States  in  1907  is  given  as  $1,280,000,000;  the  losses  from  insect  depre- 
dation? would  therefore  represent  an  annual  loss  in  a  cash  value  of 
more  than  $100,000,000. 

Reduction  in  valve  of  finished  and  commercial  products. — When 
we  consider  the  aggregate  loss  to  the  manufacturers  of  the  finished 
products,  to  the  trade,  and  to  the  consumer  from^insect  injuries  to 
the  wood,  it  is  evident  that  it  amounts  to  many  millions  of  dollars  in 
addition  to  the  estimated  loss  of  crude  products,  or  at  least  3  per 
cent  of  the  mill  value. 

sects  for  a  ten-j'ear  period,  or  an  average  of  $02,500,000  annually.  As  an  ex- 
ample, it  has  been  estimated  that  over  1,000,000,000  feet  b.  m.  of  timber  was 
killed  by  the  Black  Hills  beetle  in  the  Blacks  Hills  National  Forest  within  a 
period  of  ten  years.  This,  at  $2.50  per  one  thousand  feet  stumpage,  would  be 
an  average  of  $250,000  annually  in  a  single  forest  of  1,294,440  acres. 
[Cir.  129] 


6  INSECTS   AND  REDUCED  TIMBER  SUPPLY. 

METHODS  OF  PREVEXTIOX  AND  CONTROL. 

The  results  of  extensive  investigations  and  of  practical  applications 
of  the  knowledge  gained  during  recent  3^ears  have  demonstrated  that 
some  of  the  most  destructive  insect  enemies  of  American  forests  and 
of  the  manufactured  and  utilized  products  can  be  controlled,  and 
serious  damage  prevented,  with  little  or  no  ultimate  cost  over  that 
involved  in  forest  management  and  business  methods. 

There  are,  of  course,  certain  insects  and  certain  injuries  which, 
under  present  conditions  and  available  information,  can  not  be  con- 
trolled or  prevented,  but  it  is  very  evident  that  if  the  information 
now  available  through  the  publications  of  the  Department  of  Agri- 
culture and  through  direct  correspondence  with  its  experts  is  properly 
utilized  in  the  future  it  will  result  in  the  prevention  of  at  least  30 
per  cent  of  the  estimated  annual  waste  of  forest  resources  that  has 
been  caused  by  insects  within  recent  years,  and  thus  contribute  greatly 
to  the  conservation  of  forest  resources. 

General  Principles  of  Control. 

The  ordinary  spraying  and  similar  methods  employed  in  dealing 
with  fruit  and  shade  tree  insects  are,  of  course,  not  available  for 
practical  application  in  the  case  of  forest  trees.  But  there  are  other 
and  less  expensive  methods  of  accomplishing  the  desired  results. 

In  all  efforts  to  control  an  outbreak  or  prevent  excessive  loss  from 
forest  insects  it  should  be  remembered  that  as  a  rule  it  is  useless  to 
attempt  the  complete  extermination  of  a  given  insect  enemy  of  a 
forest  tree  or  forest  product.  Experience  has  demonstrated  that  it 
is  only  necessary  to  reduce  and  weaken  its  forces  75  per  cent  or  more. 
It  can  not  then  continue  an  aggressive  attack,  but  must  occupy  a 
defensive  position  against  its  own  enemies  until  conditions  resulting 
from  avoidable  negligence  and  mismanagement  by  the  owners  of  the 
forests  and  manufacturers  of  forest  products  favor  its  again*becom- 
ing  destructive.  Forest  insects  can  thus  be  easily  kept  under  control 
by  good  management. 

The  desired  contfol  or  prevention  of  loss  can  often  be  brought  about 
by  the  adoption 'or  adjustment  of  those  requisite  details  in  forest 
management  and  in  lumbering  and  manufacturing  operations,  stor- 
ing, transportation,  and  utilization  of  the  products  Avhich  at  the 
least  expenditure  will  cause  the  necessary  reduction  of  the  injurious 
insects  and  establish  unfavorable  conditions  for  their  future  multipli- 
cation or  continuance  of  destructive  work. 

It  is,  however,  of  the  utmost  importance  that  any  adjustment  or 
modification  in  management  or  business  methods  should  be  based  on 

ICir.  1LM>) 


INSECTS   AXD   REDUCED   TIMBER   SUPPLY.  7 

expert  technical  knowledge  or  advice  relating  to  the  species,  habits, 
life  history,  and  natural  enemies  of  the  insects  involved  and  the 
essential  features  of  the  methods  for  their  control.  This  should  be 
supplemented  by  expert  knowledge  or  advice  on  the  principles  of 
technical  and  applied  forestry  in  the  proper  management,  care,  and 
utilization  of  the  forest  and  its  resources,  and  still  further  supple- 
mented by  practical  knowledge  and  experience  relating  to  local  con- 
ditions and  facilities  favorable  and  unfavorable  for  success  in  prac- 
tical applications  according  to  the  recommended  method  or  policy  of 
control. 

As  has  been  shown,  the  mature  or  merchantable  timber  is  the  most 
susceptible  to  injury  or  death  from  the  ravages  of  insects.  There- 
fore, considered  from  the  standpoint  of  insect  control  and  the  pre- 
vention of  one  of  the  greatest  items  of  loss,  it  is  important  that  such 
matured  timber  should  be  utilized  before  it  begins  to  deteriorate,  or 
before  it  reaches  the  stage  of  unprofitable  growth. 

For  the  greatest  success  in  dealing  with  forest  insects,  it  must  be 
recognized  that  there  are  certain  features  in  the  habits  and  seasonal 
history  of  each  species  which  differ  to  a  greater  or  less  extent  from 
those  of  all  other  species,  even  of  the  same  genus;  that  there  are  cer- 
tain features  in  the  characteristics  of  the  various  species  of  trees 
which  differ  from  those  of  all  other  species;  and  that  as  a  rule  it  is  the 
technical  knowledge  of  these  peculiar  features  or  characteristics  of 
the  trees  and  their  enemies  which  furnishes  the  clew  to  successful 
methods  of  control. 

There  are  also  many  peculiar  features  in  the  prevailing  conditions 
in  different  localities,  some  of  them  favorable,  others  unfavorable,  for 
the  practical  application  according  to  a  given  method,  so  that  while 
certain  general  advice  may  apply  in  a  broad  sense  and  be  available 
for  utilization  by  the  practical  man,  whether  owner,  manager,  or 
forester,  without  further  advice,  it  is  often  necessary  to  diagnose  a 
given  case  before  specific  expert  advice  can  be  given  as  to  the  exact 
cause  and  the  most  effective  method  or  policy  to  be  adopted,  just  as  a 
l^hysician  must  diagnose  a  case  of  illness  or  injury  before  prescribing 
the  required  treatment  for  his  patient. 

Therefore,  in  a  consideration  of  the  problem  as  to  how  far  the 
waste  of  forest  resources  caused  by  insects  can  be  prevented  and  how 
far  the  damaged  timber  can  be  utilized,  we  will  attempt  to  give  only 
general  statements  based  on  the  results  of  our  observations  relating  to 
some  of  the  principal  kinds  of  loss  discussed  in  Circulars  125  to  128, 
inclusive,  of  this  Bureau.  In  addition,  we  will  consider  in  this  cir- 
cular the  utilization  of  natural  enemies  of  injurious  insects  and  the 
utilization  of  waste  caused  by  insects. 

[Clr.  129] 


UBRARY 
sT/vrc:  PLANT  BOARD 


8  IXSECTS   AND   EEDUCED   TIMBER    SUPPLY. 

Utilization  of  Natural  Enemies  and  Factors  in  the  Control  of  Inju^ous 

Insects. 

AVere  it  not  for  the  natural  checks  and  natural  factors  of  control 
of  some  of  the  more  destructive  insect  enemies  of  forest  trees  and 
forest  products,  artificial  control  would  in  many  cases  be  impossible, 
and  the  depredations  would  evidently  be  far  more  continuous  and 
complete.  These  natural  factors  in  the  control  of  the  depredating 
insects  consist  of  parasitic  and  predatorj^  insects,  diseases  of  insects, 
birds,  adverse  climatic  conditions,  etc.  '\Aliile  one  or  more  of  these 
beneficial  factors  exert  a  continuous  and  powerful  influence  toward 
the  prevention  of  a  much  greater  waste  of  forest  resources,  it  has 
been  repeatedly  demonstrated  that  they  can  not  be  depended  on  to 
prevent  widespread  devastations  or  to  otherwise  work  for  the  best 
interests  of  the  private  or  public  owner  by  protecting  the  best  trees 
and  the  best  tree  species.  The  insects  and  birds  which  prey  upon  the 
depredating  insects  also  have  factors  to  contend  against,  consisting 
of  insects,  birds,  diseases,  and  climatic  conditions.  Therefore  under 
normal  conditions  the  tendency  is  toward  the  preservation  of  a  bal- 
ance between  the  warring  factors,  but  frequently  the  enemies  of  the 
trees  get  the  ascendancy  and  take  on  the  character  of  an  invasion, 
which  may  continue  for  two  or  three  or  even  ten  years  before  the  bal- 
ance is  again  adjusted  through  the  influence  of  the  natural  enemies 
or  diminished  food  supply.  Thus  a  vast  amount  of  timber  or  of  a 
given  forest  product  may  be  destroyed  before  the  factors  of  natural 
control  can  prevail. 

It  is  evident  that  the  most  effective  utilization  of  the  agencies  of 
natural  control  will  be  through  the  alliance  with  them  of  the  owner  of 
the  forest  by  his  efforts  toward  an  artificial  reduction  of  the  enemies 
of  the  trees  rather  than  by  efforts  to  make  the  natural  enemies  of  the 
injurious  insects  his  allies  through  artificial  introduction  or  dissemina- 
tion. The  former  is  accomplished  by  the  adoption  of  methods  of  com- 
bating the  invaders  which  will  reduce  and  weaken  their  forces  below 
their  power  of  prosecuting  aggressive  movements  and  attacks,  or,  as 
previously  stated,  to  reduce  their  numbers  to  the  point  where  they 
must  occupy  a  defensive  position  against  their  natural  enemies  and  be 
dependent  for  their  supplies  of  food  and  breeding  i)laces  upon  that 
furnished  through  avoida])le  mismanagement  of  the  forests  and  manu- 
facturing operations.  Thus  the  owner  of  the  forest  can  contribute 
greatly  toward  the  preservation  of  a  balance  which  will  be  to  his 
material  benefit.  On  the  other  hand,  ho  may  in  the  future,  as  in  the 
past,  contribute  greatly  to  the  multiplication  of  the  depredating 
insects  and  to  greatly  increased  losses  caused  by  them  through  neglect 
or  a  disregard  of  available  information  on  the  fundamental  i)rin- 
ciples  of  insect  control  in  the  management  of  forests  and  manufac- 
turing enterprises. 

(rir.  12in 


INSECTS   AND   REDUCED   TIMBER  SUPPLY.  9 


BENEFICIAL    INSECTS. 


The  beneficial  insects  comprise  those  wliich  are  internal  or  external 
parasites  of  the  immature  or  mature  stages  of  the  injurious  insects, 
and  predators  which  feed  on  the  young  or  adults  of  insects  either 
before  or  after  thev  make  their  attack  on  the  trees  or  products.  These 
two  beneficial  factors  are  doubtless  far  more  effective  in  the  long  run 
than  any  other  agencies  of  natural  control.  Yet  they,  in  combination 
with  all  other  factors,  can  not  be  relied  upon  to  render  continued  and 
efficient  control.  They  can.  however,  be  relied  upon  to  respond  to 
artificial  assistance  in  reducing  the  numbers  of  the  depredators. 

BENEFICIAL  DISEASES   OF    INSECTS. 

It  is  very  evident  that  the  parasitic  fungi  and  bacteria  which  some- 
times cause  epidemics  among  injurious  insects  often  exert  a  powerful 
influence  toward  the  control  of  extensive  outbreaks  or  invasions  of 
insect  enemies  of  forests.  Indeed,  it  appears  that  the  greatest  serv- 
ice rendered  by  this  class  of  natural  enemies  is  in  the  frequent  sudden 
appearance  of  an  epidemic  which  kills  off  a  destructive  species  of 
insects  after  the  latter  has  increased  to  such  numbers  and  extended 
its  depredations  over  such  vast  areas  as  to  be  far  beyond  the  control 
of  man  or  his  insect  and  bird  allies.  Numerous  examples  of  this  kind 
of  natural  control  are  found  in  the  sudden  ending  of  widespread 
depredations  by  various  species  of  caterpillars  and  sawfly  larva?  which 
defoliate  deciduous  and  coniferous  trees.  As  a  rule,  however,  the 
beneficial  effects  of  the  diseases  of  insects  prevail  only  after  the 
injurious  insects  have  increased  to  excessive  numbers.  Therefore  this 
factor  of  insect  control  can  not  be  depended  upon  to  hold  the  insects 
in  check  or  prevent  outbreaks.  The  fact,  however,  that  it  operates  on 
a  class  of  insect  enemies  of  the  forest  (defoliators)  which  at  present 
can  not  be  controlled  by  any  known  artificial  methods  renders  the 
services  of  the  diseases  all  the  more  valuable. 

It  is  believed  that  with  further  knowledge  of  nature's  method  of 
propagating,  perpetuating,  and  disseminating  the  diseases  which 
cause  epidemics  among  insects  they  may  be  utilized  more  or  less  suc- 
cessfully through  artificial  propagation  and  dissemination  to  prevent 
threatened  invasions  of  defoliating  insects. 

BENEFICIAL    BIRDS. 

It  is  very  evident  that  certain  kinds  of  birds,  such  as  woodpeckers, 
render  valuable  service  toward  the  natural  control  of  destructive 
bark  and  wood  boring  insects.  They  appear  to  render  the  greatest 
service,  however,  where  but  few  trees  are  being  killed  or  injured, 
because  their  concentrated  work  on  such  trees  may  contribute  toward 
the  prevention  of  an  abnormal  increase  of  the  insects.     They  also 

[Cir.  129] 


10  IXSECTS   AXD  REDUCED  TIMBER   SUPPLY. 

render  some  service  as  allies  of  the  other  beneficial  factors  which  assist 
in  artificial  control.  It  is  evident,  however,  that  where  many  hun- 
dreds or  thousands  of  trees  are  being  killed  the  comparatively  limited 
number  of  birds  in  any  forest  under  the  most  favorable  conditions 
could  have  little  or  no  beneficial  effect.  Therefore,  while  the  birds 
should  be  classed  among  the  valuable  friends  of  the  forest,  and  should 
be  protected,  it  "is  plain  that  they  can  not,  even  with  the  utmost  pro- 
tection, be  relied  upon  to  protect  the  forest  against  destructive  ravages 
of  insects. 

We  must  remember,  in  this  connection,  that  there  are  complicated 
interrelations  between  birds,  injurious  insects,  and  beneficial  insects 
which  do  not  necessarily  operate  to  the  benefit  of  the  forest.  In 
fact,  it  may  sometimes  be  quite  the  reverse.  Therefore,  in  order  to 
derive  the  greatest  benefit  from  the  conflict  between  the  birds,  the 
insect  enemies  of  the  trees,  and  the  insect  friends  of  the  trees,  we 
must  utilize  our  knowledge  of  the  factors  which  are  contributing 
toward  the  preservation  of  a  balance,  so  that  whenever  the  enemies 
of  the  forest  threaten  to  get  beyond  natural  control  we  may  enter  the 
field  through  artificial  means  and  endeavor  to  force  them  back  to 
their  normal  defensive  position. 

BENEFICIAL  CLIMATIC  CONDITIONS. 

The  benefits  to  be  derived  from  climatic  conditions  which  are  detri- 
mental or  destructive  to  insect  enemies  of  the  forest,  while  some- 
times very  great,  are  necessarity  unreliable,  and  thus  can  not  be 
depended  upon  to  assist  in  artificial  control.  In  fact,  the  very  condi- 
tion which  may  contribute  to  the  destruction  of  one  depredator  may 
favor  the  multiplication  of  another. 

Utilization  of  Waste  Caused  by  Insects. 

"\Mien  we  come  to  consider  the  vast  amount  of  standing  timber  in 
the  forests  of  the  country  which  has  been  injured  or  killed  by  insects, 
and  will  go  to  waste  if  it  is  not  utilized  within  a  limited  period,  we 
realize  that  there  are  great  possibilities  in  its  utilization  as  a  means 
of  preventing  the  reduction  of  future  supplies  of  living  healthy  tim- 
ber. It  is  all  the  more  important  that  the  insect- infested  timber 
should  be  utilized,  because  in  so  doing  we  can  contribute  more  per- 
haps than  in  any  other  way  to  the  reduction  of  the  insects  to  or  below 
their  normal  numbers,  and  thus  provide  against  serious  injury  in  the 
future,  as  well  as  to  the  maintenance  of  control. 

Approved : 

James  Wilson, 

Secretary  of  Agiicidture. 
Washington,  D.  C.,  October  7,  1010. 

[Clr.  1.29] 

o 


UNIVERSITY  OF  FLORIDA 

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3  1262  09228  3158 


